In many operations it is desirable or necessary to extract or remove a liquid mist or liquid particles from a gas stream in which the liquid mist or liquid particles are suspended or entrained. In some cases mist eliminators are used for the cleaning of waste or a dirty gas stream in a wet scrubber or other application, since the gas stream must be free or substantially free of the entrained liquid or mist before the gas stream can be discharged or used. In other cases the liquid forming the mist or liquid particles entrained in the gas stream is in itself useful and it is desired to remove the mist or liquid as a recovery product of the gas stream. In such operations mist eliminator devices are provided to remove or entrain liquid or mist from a mist-rich gas stream to provide a mist-lean gas stream.
Such mist eliminators include structured packing or packed beds wherein the structured packing or baffles employed are arranged in a zigzag or other configuration so as to provide for a zigzag or a tortuous flow path for the gas stream. It is desirable to have the gas stream change direction several times as it passes through the mist eliminator devices so that upon a change in the direction of the gas stream the mist or liquid particles impinge upon the surface of the baffle members, coalesce on the surface, and fall or drain downwardly out of the gas stream. Typically mist eliminator devices contain one or more layers of sheet-type baffles, such as C, S, W or Z blades, arranged in a zigzag, closely packed configuration. These eliminator devices usually comprise a plurality of baffle members in a spaced apart, generally parallel arrangement with gas passages between the individual baffle members to create the tortuous gas flow path. The baffle members typically have an upstream and downstream edge.
Generally, a layer of chevrons is placed in single or multiple layers across the diameter of a column and in such vertical flow chevron-type devices the liquid collected from the upwardly flowing gas stream must be removed from the chevron devices and typically drains down against the upwardly flowing gas streams. At high gas velocities the drag of the gas stream on the downwardly flowing liquid prevents good liquid drainage from the chevron-type baffles. At sufficiently high gas velocities (above the critical velocity or maximum allowable velocity) liquid accumulates on the chevron-type baffle surface and often between the closely spaced baffle members and some reentrainment of the liquid then occurs with the upwardly flowing gas stream.
The maximum gas capacity of a vertical flow chevron-type baffle mist eliminator is typically limited by the onset of reentrainment of the coalesced droplets back into the upwardly flowing gas stream downstream of the chevron device. It is desirable, therefor, to provide for an improved chevron-type mist eliminator and to prevent or reduce the reentrainment of coalesced droplets back into the upwardly flowing gas stream and to increase the critical velocity of the gas stream and gas capacity of the chevron-type device and to decrease the pressue drop across the mist eliminator.